The present invention relates generally to drive apparatus for an optical system of video cameras or the like, and more particularly to a lens drive apparatus suitably applicable to a camera having the auto-focusing function and the zooming function. In addition, this invention relates to a control apparatus for controlling the drive of an optical system of a camera.
Various auto-focusing techniques for use in video cameras or the like have hitherto been proposed which automatically brings the video camera into focus over a wide range. These auto-focusing techniques are generally arranged to bring the camera into focus by moving a portion of an optical system of the camera by a motor in directions along the optical axis of the optical system. However, in cases where the auto-focusing operation is efected by moving the rear side of the optical system, difficulty is encountered to offer the manually operated focusing function to such a camera. That is, because the lens to be moved for the focusing is positioned at the rear side of the optical system, the lens tends to be covered by a housing of the camera so as to make it difficult to manually perform the focusing operation. For eliminating this problem, a small rotatable control can be provided at the housing so as to effect the manual focusing by rotating the small rotatable control by hand, while such an arrangement involves a difficulty to offer a mechanically hand-operated sensation for the user as obtained in a still camera.
Further, in the camera having the focusing function and the zooming function, at least one of the focusing and zooming operations is generally achieved by moving the optical system of the camera by the driving force due to a pulse motor such as disclosed in the Japanese Patent Provisional Publication No. 60-143309 or 63-33720. The movement of the optical system for the focusing or zooming operation is generally effected through a manual switch which is arranged to perform the ON/OFF operation of the pulse motor. In this case, the drive of the pulse motor is effected by a motor drive pulse signal with a constant period which is outputted from a control circuit in correspondance with the ON state of the manual switch, whereby the movement of the optical system is made at a constant speed at the time of the manual operation. However, according to this arrangement, difficulty can be encountered to meet the requirement to perform a fine adjustment to be required at the vicinity of the focusing position. In order to remove this problem, an optical system drive apparatus is known which is equipped with a signal generating means which is arranged so as to generate information including the moving direction and moving amount of the optical system in accordance with the rotational operation mode of a manual ring for the adjustment of the optical system. However, because the rotational operation mode of the manual ring is varied by each user, there is the possibility that the motor drive pulse signal has a frequency above the pulse motor responsible frequency, for instance. In this case, the moving amount of the optical system due to the pulse motor cannot be coincident with the adjustment amount due to the manual ring.